American scientists Jeffrey C Hall, Michael Rosbash and Michael Young have been awarded the 2017 Nobel Prize in Physiology or Medicine “for their discoveries of molecular mechanisms controlling the circadian rhythm"—the internal body clock that regulates our sleep patterns and helps us adapt to day and night cycles.

Circadian rhythms anticipate day and night cycles in order to optimize the behaviour of organisms accordingly—humans, for example, sleep during the night and wake during the day.

Scientists have long known circadian rhythms exist and are important to the physiology and behavior of an organism. However, how this worked on a genetic level was not known.

In the 1980s, Hall, Rosbash and Young isolated and characterized the period gene—a gene that explained changes to the regular 24-hour cycle of fruit fly larva hatching from their eggs. Over the following years, the three scientists made a series of breakthroughs that would lead them to identify other genes that partner with the period gene, eventually leading to the discovery of molecular mechanisms of the circadian clock.

Once they had identified these mechanisms, scientists realized there was a “complex network of reactions” that take place within the body that the circadian rhythm is involved with, including body temperature, blood pressure, hormone release, metabolism and sleep patterns.

Disruption to the normal circadian rhythms of humans has been linked to a range of mental health disorders, including depression, bipolar disorder, memory formation and a range of neurological conditions. It can also lead to diseases such as cancer, metabolic disorders and inflammation. Understanding this had the potential to help improve the health of people whose sleep cycles are permanently disrupted, such as those who work shifts.

“The seminal discoveries by Hall, Rosbash and Young have revealed a crucial physiological mechanism explaining circadian adaptation, with important implications for human health and disease,” the Nobel Prize organizers said in a statement.

Last year, the prize was awarded to Yoshinori Ohsumi for discovering the mechanisms underlying autophagy—the process where cells degrade and recycle. The concept of autophagy was proposed in the 1960s but was very difficult to prove. Ohsumi’s experiments using baker’s yeast provided the underlying processes and he was then able to show how similar events take place in our own cells. The discovery opened up a new way of understanding many physiological processes, including how cells respond to infection and how genes can cause disease, including cancer.